Many industrial processes require equipment that is capable of automatically controlling supplies of gases and fluids. The fabrication of integrated circuits generally includes a process such as chemical vapor deposition in which a variety of heated gases is introduced into a partially evacuated chamber confining a semiconductor substrate. By carefully managing the temperature and pressure within this enclosure, various layers of conductive, insulative, and semiconductive materials are grown on the substrate to create the three-dimensional circuit patterns of an integrated circuit. All of the substances that are transported in and out of the chamber must be constantly monitored, since the proportions of the different reactants that constitute the vapor atmosphere ultimately determine the physical dimensions of the transistors, capacitors, and resistors that will collectively comprise a single, vast electrical circuit on a tiny chip of silicon. One of the greatest causes of failures of finished integrated circuits is attributable to microscopic dust particles that contaminate the workspace where the chip is manufactured. Since even one tiny foreign body can ruin a very expensive chip, semiconductor makers fabricate their products in a "clean room" environment that guards against such contamination. The air which is admitted into a clean room is first passed through an extensive filtration system that virtually eliminates unwanted dust particles. Technicians who work within these facilities wear special clothing and masks that prevent the introduction of substances that would interfere with their meticulous work. The cost of building, maintaining, and operating this highly specialized environment is enormous. Consequently, all the space within a clean room must be utilized as efficiently as possible. All the equipment that is used within the confines of the clean room should occupy as small a volume as is practical. In addition to this critical need for miniaturization, the chemicals employed in the vapor deposition method must be housed and conveyed with great care. The solvents, acids, oxidizing agents, and other substances used in the semiconductor laboratory are often caustic or toxic. The devices that are selected to conduct these potentially hazardous materials should be capable of providing reliable service free from wear, corrosion, or leakage.
In U.S. Pat. No. 4,989,160, Garrett et al. applied modular process control hardware to rather conventional gas control devices, using widely accepted instrumentation and control techniques. While such methods begin to deal with some of the improvements needed in gas management control, they have failed to address many of the design shortcomings of gas management systems.
Gas manifolds in present systems commonly use stainless alloy tubing and swaged fittings to supply the connections between manifold components, such as valves, regulators, and pressure sensors. These complex assemblies of tubing and fittings suffer from a high parts count. The gas manifolds are large and bulky, and the large, internal gas volume results in large purge times, with an excess waste of costly purge gases. The large volumes of potentially hazardous process gases to be purged create safety and disposal problems when the process gases are purged from the system. Tubing and fitting assemblies are also prone to leakage from improper assembly, service, or damage during use.
Previous solutions such as those offered by Garrett et al. have also failed to improve upon the safety, cost, and extensive downtime for the service of manifolds or controls. These systems are installed integrally within the large gas system containment cabinets. When preventative maintenance, calibration or repair is required, the system cabinet must be taken off line for a prolonged period of time. Service personnel are then required to perform all service tasks with the equipment in position, within the clean-room environment. This is an inefficient environment for equipment service, and can pose safety risks from exposure to process gases during this service interval.
Since the entire manifold and control are integral with the cabinet, the increased risk of contamination to the clean-room area by these non-manufacturing service activities is unavoidable. Should a particular gas cabinet be disabled for a prolonged period, the only way that manufacturing can be resumed in areas that had relied upon that gas management device is if another large and costly gas cabinet has been installed to provide appropriate levels of redundancy.
Previous gas cabinet systems that have been incorporated into chip fabrication systems have served the needs of semiconductor manufacturers adequately, but at a high cost in terms of the great space and volumes that they occupy. The shortcomings of conventional gas control devices has presented a major challenge to designers in the field of industrial controls. The development of a miniaturized, modular, safe, and clean gas management system that provides intelligent automated control for integrated circuit fabrication would constitute a major technological advance. The enhanced performance that could be achieved using such an innovative device would satisfy a long felt need within the computer industry.